The invention relates to an optical lens, a method of manufacturing an optical lens system, an optical scanning device for scanning an information layer of an optically scannable information carrier, and a an optical player for scanning an information layer of an optically scannable information carrier.
An optical player, an optical scanning device employed in the player, and an optical lens system used in the scanning device, of the types mentioned in the opening paragraphs are known from EP-A-0 863 502. The first lens of the known lens system is an objective lens, and the second lens is an auxiliary lens arranged between the objective lens and the information carrier to be scanned. By using the auxiliary lens, the known lens system has a comparatively large numerical aperture, as a result of which a relatively small scanning spot is formed on the information carrier to be scanned. The known scanning device can thus suitably be used to scan information carriers having comparatively small elementary information characteristics, i.e., information carriers having a comparatively high information density, such as a high-density CD. The first and the second lens are provided with ring-shaped flanges, each flange being manufactured in one piece with the associated lens body and provided with, respectively, a ring-shaped and a circular cylindrical positioning surface. The first mount of the lens holder includes a ring-shaped positioning surface, which extends perpendicularly to the centerline of the lens holder, and against which the ring-shaped positioning surface of the first lens abuts. The second mount of the lens holder also includes a ring-shaped positioning surface which extends perpendicularly to the center line and which surrounds the first lens and abuts against the positioning surface of the first mount, and a sleeve whose inner wall is concentrically arranged around the center line, the circular cylindrical positioning surface of the second lens being in contact with said inner wall. The optical axes of both lenses should coincide within predetermined comparatively close tolerances so as to make sure that a proper optical effect of both lenses is achieved. To this end, the optical axes, viewed in directions perpendicular to the centerline, must be accurately positioned with respect to each other and must extend accurately parallel to one another. In the manufacture of the known lens system, the positions of the optical axes relative to each other can be corrected in directions perpendicular to the center line by moving both mounts with respect to each other over their positioning surfaces. Parallelism of the optical axes is achieved by providing the ring-shaped positioning surface of the first lens at right angles to the optical axis of the first lens, and by providing the circular cylindrical positioning surface of the second lens so as to be concentric with respect to the optical axis of the second lens.
A drawback of the known lens system, the known optical scanning device and the known optical player resides in that the comparatively close tolerances within which the optical axes of the two lenses of the lens system must coincide are comparatively very difficult to achieve. This can be attributed to the fact that the provision with the desired accuracy of said positioning surfaces on the flanges of both lenses is a very laborious process.
It is an object of the invention to provide a lens system, an optical scanning device and an optical player of the types mentioned in the opening paragraphs, in which the comparatively close tolerances within which the optical axes of the two lenses of the lens system must coincide can be achieved in a less laborious way.
To achieve this object, a lens system in accordance with the invention is characterized in that the first and the second mount comprise, respectively, a first and a second circular cylindrical inner wall having a common center line, a diameter of the first inner wall and a diameter of the second inner wall being substantially equal to, respectively, the first and the second diameter, and the first and the second lens comprising more than one half of, respectively, the first and the second spherical lens body.
To achieve this object, an optical scanning device in accordance with the invention is characterized in that the lens system used therein is a lens system in accordance with the invention.
To achieve this object, an optical player in accordance with the invention is characterized in that the optical scanning device used therein is an optical scanning device in accordance with the invention.
As the diameters of said inner walls are substantially equal to, respectively, the first diameter of the first lens body and the second diameter of the second lens body, both lenses are accurately positioned in both mounts in directions perpendicular to the centerline. A very accurate mutual positioning of both lenses in directions perpendicular to the center line is achieved in that the diameters of said inner walls are accurately dimensioned and said inner walls are very accurately coaxial. This accuracy can be achieved in a manner which is not very laborious by providing the first and the second mount of the lens holder with, respectively, the first and the second circular cylindrical inner wall using conventional tools, such as a lathe. Also the spherical lens bodies can be very accurately manufactured using comparatively simple processes, such as rolling process. Since the first and the second lens comprise more than half the, respectively, first and second spherical lens body, both lens bodies, after having been positioned in the two mounts, can still be tilted through limited angles in both mounts around the center of the relevant lens body, without the mutual positions of the two lenses, viewed at right angles to the center line, being influenced, so that the accurate mutual positions of the two lenses, viewed at right angles to the center line, is not influenced when, at a later stage, the optical axes of the two lenses are adjusted so as to be parallel.
A particular embodiment of an optical lens system in accordance with the invention is characterized in that the first lens is bounded, on a side facing the second lens, by a boundary surface extending perpendicularly to the center line, while the first mount is provided with an abutting member for the boundary surface of the first lens, which abutting member extends in a plane perpendicular to the center line. Said boundary surface and said abutting member cause the optical axis of the first lens to be accurately situated parallel to the centerline of the lens holder. Said boundary surface only must be accurately flat, the optical axis of the first lens being formed by the diameter of the first lens body extending perpendicularly to the boundary surface. Said abutting member must be accurately provided so as to extend perpendicularly to the center line of the lens holder, which can be carried out in a manner which is not very laborious by using conventional tools, such as a lathe.
A further embodiment of an optical lens system in accordance with the invention is characterized in that the abutting member comprises a ring-shaped surface extending perpendicularly to the center line, which ring-shaped surface causes the first and the second inner wall to be connected to one another in a stepwise manner. In this embodiment, the abutting member is embodied in a manner which is both practical and not very labor-intensive.
Yet another embodiment of an optical lens system in accordance with the invention is characterized in that the second lens is bounded, on a side facing away from the first lens, by a boundary surface extending perpendicularly to the centerline. Said boundary surface only must be accurately flat, the optical axis of the second lens being formed by the diameter of the second lens body extending perpendicularly to the boundary surface. Since the boundary surface is provided on the side of the second lens facing away from the first lens, the boundary surface is accessible to an aligning tool in a manner which is not very laborious, which aligning tool serves to make sure that the optical axis of the second lens extends parallel to the center line of the lens holder.
A particular embodiment of an optical lens system in accordance with the invention is characterized in that the second mount is provided, on a side facing away from the first lens, with an end surface extending perpendicularly to the center line, the end surface and the boundary surface of the second lens being situated in a common plane. In this particular embodiment, said end surface is provided so as to extend perpendicularly to the center line of the lens holder, which can be achieved in a manner which is not very laborious by using conventional tools, such as a lathe. Parallelism of the optical axis of the second lens and the center line can be readily adjusted using aligning tools provided with a common aligning surface for said end surface and the boundary of the second lens.
A further embodiment of an optical lens system in accordance with the invention is characterized in that at least one of the two lenses is secured in the relevant mount by means of a glued joint. Said glued joint is very simple and can be provided, after the relevant lens has been aligned with respect to the relevant mount, without influencing said position of the relevant lens with respect to the relevant mount.
A still further embodiment of an optical lens system in accordance with the invention is characterized in that at least one of the lenses is secured in the relevant mount by press-fitting the relevant lens body in the relevant inner wall. In this manner, the relevant lens is secured in the relevant mount in a very simple and reliable manner.
A particular embodiment of an optical lens system in accordance with the invention is characterized in that the first and the second mount are substantially sleeve-shaped and connected to one another via a hollow conical center portion of the lens holder. The use of said conical center portion provides the lens holder with a very high rigidity and accuracy of form, viewed in a direction parallel to the centerline, so that the mutual positions of the two lenses are substantially uninfluenced by lens holder deformations.
A method of manufacturing an optical lens system in accordance with the invention is characterized in that the second lens is positioned in the second mount by supporting the boundary surface of the second lens by means of a first aligning surface of an aligning tool, and by simultaneously supporting the abutting member of the first mount by means of a second aligning surface of the aligning tool that is directed parallel to the first aligning surface. The abutting member of the first mount is intended for the boundary surface of the first lens and extends in a plane that is perpendicular to the centerline of the lens holder. By simultaneously supporting the boundary surface of the second lens and said abutting member by means of the two parallel aligning surfaces of the aligning tool, the optical axis of the second lens is accurately positioned parallel to the center line of the lens holder. By positioning, at a later stage, the boundary surface of the first lens so as to be in contact with said abutting member, also the optical axis of the first lens is accurately positioned parallel to the center line of the lens holder. In this manner, the optical axes of the two lenses are positioned parallel to the center line in a manner which is not very laborious by using said aligning tools. To achieve the desired parallel positions of the two lenses, the lens holder only has to be provided with a single, accurately provided abutting member.
A further method of manufacturing an optical lens system in accordance with the invention is characterized in that the second lens is positioned in the second mount by simultaneously supporting the boundary surface of the second lens and the end surface of the second mount by means of an aligning surface of an aligning tool. In this further method, the lens holder is provided with an abutting member for the boundary surface of the first lens, which abutting member extends perpendicularly to the center line, and with an end surface for cooperation with the aligning surface of the aligning tool, which end surface extends perpendicularly to the center line. The necessary aligning tool has to comprise only a single aligning surface and hence is of a very simple construction.